Dynamo-electric machine.



A. HILL.

DYNAMO ELECTRIC MACHINE.

APPLIOATION FILED FEB. 23, 1911.

Patented Sept. 2; 1913.

fnwnl'or.

unrrnn STATES PATENT cri ical ABhTEB HILL, 0]? WARMINSTER, ENG LAND;ASSIGNOR TO TRIER AND MARTIN LIMITED, OF I'IONDON, ENGLAND..

DYNAMO-ELECTRIlCI MAGHINE.

Specification of Letters Patent.

Patented Sept. 2, 1 9-1 3.

Application filed February 23, 1911. Serial No. 610,247.

To all whom it mag concern:

Be it known that I, ABNnn HILL, subject "-of the King of England,residing at arininster, in Wiltshire, England, have invented certain newand useful Improvements in Dynamo-Electric Machines, of which thefollowing is a specification.

This invention relates to dynamo electric machines designed to giveapproximately constant current over a large range of speed and of thetypein which auxiliary brushes are used.

Various arrangements have been proposed for modifying the characteristicof a dynamo by the provision: of auxiliary brushes connected to eachother or to the main brushes through field magnet windings or otherwise,and it is to this general class that the present invention belongsv Ithas been suggested to employ auxiliary brushes: connectedto the main.brushes through fixedv or variable resistances in order to transformthe demagnetizing force of the armatureinto' a magnetizing force andform a zone of commutation extending symmetrically on each side of theneutral line so that the-machine may run sparklessly. at various loadswith the brushes in one position. It has also been proposed to employshort-circuited-brushes in a dynamo I wherein, in order to-obtain anexternal ourrent always in one direction,= the working nagnetic field isproduced by the armature andvaries in direction with the direction ofrotation. I i

According to this invention, the main brushes, which are'in theordin'aryorneutral position, are each joined through an external resistance, thatis to say, not through a fieldanagnet winding, toanauxiliary brush halfa pole-pitch inadvance, the arrangement being such that part of the maincurrent at high speeds is supplied by the auxiliary brushes.

In the following description, the invention is described as applied to atwo-pole machine although it will. be understood that it is equalyapplicable to machines having a large number of poles.

The accompanying drawing shows diagrammatically a dynamo electricmachine according to th1s invention. By way of example a two-pole dynamois shown having a ring armature A driven 1n the direction indicated bythe arrow a and field magnets B having pole pieces B The main orordinary brushes are indicated at C and C and are set in the ordinary orneutral position. The main brush C is connected through an externalresistance E to. an auxiliary brush D which. is in advance of the mainbrush by about 90, and the main brush C is simi larly connected throughan external resist ance E to a second auxiliary brush D The amount ofthe resistance E will vary in accordance with the general design of themachine and it may be divided and be capa-.- ble of adjustment in anyknown manner.

The field magnets B are exeited by shunt coils F connected across themain brushes C,.C As O is thefnegative and C the positive-brush, thecurrent in the resistance connecting the main brush C with the auxiliarybrush. D will, when the machine is running on open circuit, flow from Cto D and, in the resistance connecting the other pair of brushes, willflow from D to C. The effect of these currents, which of course alsoflow in the armature coils between D and E ia-and C and D, is tostrengthen thefinain As the load increases an armature reactionis set upwhich displaces the axis of the field forward and by.so doing reducesthe current in the resistances E and consequently the magnetic field isalso reduced. When the axis of the magnetic field is dis placed" by45.", there will be no current at all between the main and auxiliarybrushes as theywill then be at equal potentials. A further displacementof the magnetic field due to increasing load and speed will cause acurrent to flow again between the main and auxiliary brushes, but suchcurrent will now be in the reverse direction and its effect will be toweaken the main field instead! of to. strengthen it. Thus the output ofthe dynamo becomes self-regulating.

By suitably designing the machine it is possible to arrange that, whenthe dynamo is just running at sufiicient speed to give the voltage forwhich it is intended but no current in the external circuit, thecurrents in the resistances E will be approximately equal to half thefull-load current for which the dynamo is constructed. As the machinebegins to give current to the external circuit, the currents in theresistances E drop until at about half-load there is no current flowingthrough them and the machine is then working as an ordinary shuntdynamo. As the speed and load further increase, reverse currents beginto flow in the resistances E, and when the dynamois giving its full-current, about half of that current is supplied from the auxiliary brushes.This has the efl'ect of giving a very uniform watt loss in the armaturecopper over the whole speed range, and, as at full-load the current ineach resistance E is equal to about half the total current, the armaturecoils between the main and the auxiliary brushes are practically idle.Thus, the watt loss in the armature copper will then be only half ofwhat it would be with an ordinary dynamo and consequently, for a givenload, it is pos -main brushes, each auxiliary brush being disposed halfa pole pitch in advance of amain brush and external resistancesconnecting each main brush with the auxiliary brush in advance of it,the arrangement being such that as the load increases and consequentlythe axis of the magnetic field is displaced, the currents in theresistances are reversed and at heavy loads are in such a direction thatpart of the main current is supplied by the auxiliary brushes.

2. In a self regulating dynamo, the combination with field magnets, ofan armature rotatable in the magnetic field, a plurality of main brushessituated in the neutral line, a plurality of auxiliary brushescorresponding in number to the main brushes, each auxiliary brush beingpermanently disposed half a pole pitch in advance of a main brush andsubstantially constant external resistances connecting each main brushwith the auxiliary brush in advance of it, the arrangement being suchthat at rated voltage and open external circuit said resistances carryabout one half the full load current of saiddynamo and at abouthalf-load no said armature and field being relatively rotatable, mainbrushes for the armature, an auxiliary brush for each main brush, andconnecting means includmg a resistance between each main brush and theauxiliary brush associated therewith, each main brush and the auxiliarybrush connected therewith being permanently spaced apart substantiallyhalt a pole pitch, for the purpose set forth. 7

Y 4. In a self regulating generator designed to supplyapproximatelyconstant current over a widerange of speed, the combinationof field poles and windings on said poles for producing a magneticfield, an armature rotatable in said field, current supply mains, mainbrushes for the armature disposed in the ordinary or neutral positionand connected to said supply mains, an auxiliary brush associated witheach main brush, means connecting the auxiliary brush with itsassociated main brush and a sup-" ply main, a substantially constantresistance in circuit with said connecting, means, each auxiliary brushbeing disposed substantially half a pole pitch in advance of the mainbrush connected therewith, the arrangement being such that when thearmature is rotated at a speed sufiicient to generate substantiallyno-load current at normal voltage the current in said connecting meanswill flow in one direction and when the armature supplies current inexcess of about half the output of the generator the flow of currentinsaid connecting means will be reversed and part of the armature currentwill flow through said auxiliary brushes.

In testimony whereof I have signed my name to this specification in-thepresence of two subscribing witnesses.

ABNER HILL. Vitnesses FRANK TRIER, R. W. MIAMS.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents,

Washington, D. C. i

